Nonmetallic sheathed multiple-conductor cable



June 12. 1928. 1,673,752

E. H. LEWIS ET AL NONMETALLIC SHEATHED MULTIPLE CONDUCTOR CABLE FiledJune 28, 1927 Ru lab 61" IYM/QntOrsl Edward H. Lew i s.

C! ifforcl O. HUI I.

Their Atton ey.

Patented June 12, 1928.

UNITED STATES PATENT OFFICE.

EDWARD H. LEWIS; OF BRIDGEPORT, AND CLIFFORD O. HULL, OF NEWIBRIDGEPORT, CONNECTICUT, ASSIGNORS TO GENERAL ELECTRIC COMPANY, ACORPORATION OF N EW YORK.

NONMETALLIO SHEATHED MULTIPLE-CONDUCTOR CABLE.

Application filed June 28, 1927. Serial No. 202,135.

The present invention relates to multiple conductor cables for conveyingelectric current for various purposes at the potentials commonlyemployed in buildings -f usual construction. These cables must be ofsuch a character that they can be installed in all sorts of places, someof which may be dry and others damp. The insulation must be of such acharacter that the conductors are well insulated from each other andfrom any metal or grounded part with which the cable may come incontact. Further, the insulation must be as nearly fire proof aspossible so as to withstand heating due to .heavy currents, as shortcircuits for example, or external heating due to any cause.

Desirable qualities of the cable are that it be capable of being bent atrather sharp angles without injury to the conductors or theirinsulation; that the insulation, especially the outer coating, be highlyresistant to injury whenthe cable is being installed by being drawn overrough beams,-etc.;' that the cable shall have high tensile strength soas to prevent stretching of the insulation with the result of weakeningit; and that the various parts of the insulation be so arranged orassembled that they may readily be removed from the conductors by thewireman preparatory to making electrical connections of the usualcharacter.

The object of our invention is the provision of a noneme'tallic sheathedmultiple conductor cable of improved construction which will have amongother things all of the necessary and desirable qualities aboveenumerated.

For a consideration of what we believe to be novel and our invention,attention is directed to the accompanying description and the claimsappended thereto.

In the attached drawing which is illustrative of ourinvention, Fig. 1 isa view on an enlarged scale of a two conductor cable, partlyin section;Fig. 2 is an end view of the same, and Fig. 3 is an end view of a threeconductor cable, also on an enlarged scale.

In Figs. 1 and 2, 5 and 6 are tinned copper conductors, each of which issurrounded by an insulating body 7 made of suitable rubber or rubbercompound. The rubber covering should be of a character to Withstand highvoltage, say of the order of 1500 volts, for a limited time when theconductor and its covering 'is immersed in water. Surrounding the rubberbody is a cotton braid covering 8. The braid coverings on the twoconductors differ in color polarity of the conductors may be determinedby the wireman and the proper con-' .nections made. For example, thebraid covering for conductor 5 may be White and that for conductor 6black. Where a third conductor is employed, as in Fig. 3, it has a stilldiflerent colored braid as red for example. The braid covering in eachinstance is given a thin protective coating of wax. For the white braidwe use zinc oxide and Wax 9 and wipe it smooth, the color of theprotective coating in each case corresponding generally to the color ofthe braid. The purpose of the wax is threefoldit prevents the saturatingcompound used on the next outer insulating layers from penetrating thebraid and causing it to lose its distinguishing color, it water-proofsthe braid, and finally, it revents the next outer layer of insulationrom adhering so closely to the braid that it can only be removed withdifficulty. The last mentioned feature is of material advantage to thewireman who has to strip the conductors of their insulation beforeelectrical connections can be made.

Over the braid and its protective wax coating is spirally wound twolayers of jute 10 and 11, one layer being applied right handedly and theother left. These layers are applied simultaneously and each comprises aplurality of separate cords or elements, eight in the present instance,which are wound in multiple. When so applied the turns in. each layerare in contact with each other so as to form a complete covering Withoutintervening spaces. Due to the fact that the outer layer is of largerdiameter because it surrounds the first, to the fact that the two layersare Wound simultaneously, and to the fact that the turns must be inside-wise contact to form a complete covering, the cord used in thesecond or outer layer is made of slightly larger cord. The weights ofthe Wraps may be of the order of six-pound dry jute for the inso thatthe nor wrap and eight-pound dry jute for the outerwrap. The cordwrapping is made of jute because of its good insulating properties, butit has one disadvantage; namely, that a large number of small fiberswill project outwardly therefrom in all directions beyond the diameterof the cord and overlie the adjacent cords or turns on both sides. Theseprojecting fibers while individually small form in the aggregate asubstantial body and after the cords have been treated with a binder orcompound will unite the cords quite firmly. This particular union is adistinct disadvantage from the standpoint of the wireman because itmakes it so much more difficult to' -emove'the cords and otherinsulation prior to making an electrical connection. To avoid this theconductor afterv receiving its two jute wrappings or ribbons is-passedthrough a gas flame to singe off the loose projecting fibers abovereferred to, and in this'manner the objectionable binding ofcord-to-cord is obviated. The singeing operation is chiefly confined tothe outer layer but this sufiices for the purpose. With the fibersremoved the wireman can easily unwind the cords or he may to a largedegree remove them by an endwise pull,- after which the inner ends ,of

those portions can be cut with a knife.

After the jute wraps are applied and singed they are treated with aflame-proof compound or saturator 12 of a characterv having an asphaltbase. The compound or saturator is applied at high temperature, say ofthe order of 500 F. after which the surface of the jute wrapping isclosely wiped to remove any excess material and also to render thesurface as smooth as possible. This treatment is of such a nature thatthe outer jute layer is thoroughly impregnated and the inner layer to alesser extent so as not to seriously interfere with the strippingoperation by the wireman. The wax coating on the braidbelow the innerjute covering softens during the singeing and slightly penetrates theimmediately surrounding jute with the result of assisting to prevent thecompound from completely impregnating it. The wax as previously statedalso prevents the compound from discoloring the identifying braid on theconductor and facilitates stripping the jute insulation from theconductor. Due to the fact that there is less compound on the inner jutelayer than on the outer the small fibers projecting therefrom do notadhere as strongly as would otherwise be the case. After the'juteWrappings have been treated as above outlined they are given a thinprotective coating of crude scale wax 13 and then wiped to remove theexcess, care being exercised, how-. ever, to see that a substantial filmof wax is permitted to remain. The melting point of this crude scale waxwhich has a parafiine base is substantially lower than that of thecompound or saturator, and is applied at a lower temperature, say of theorder of 120 F. After the two conductors have been insulated as abovedescribed they areassembled side by side and in close contact. In thespaces on each side of the region of contact of the conductors arelocated longitudinal members 14: and 15 also made of twine or jute andwhich have been treated with crude scale wax. These form fillers toround out the outer surface of the cable and by making them relativelyhard they also prevent the cable, including of course the insulation,from kinking "when sharply bent. As previously stated these cables whenbeing installed are subjected to considerable longitudinal strain due tothe pulling operations. .Therefore,,in order, to add strength to thecablethe fillersare made of substantial strength, say of the order ofone Of the metal conductors. The fillers may advantageously be made ofwhat is known as Nassau twine for the smaller sizes and of dry jute forthe larger sizes.

' As above stated, the jute wrappings are given a thin coat of wax whichacts to prevent the] outside or over-all braid from sticking too closelythereto. For this purpose the material known as scale wax may beadvantageously employed. It is a form of paraffin wax and has a lowermelting temperature than the compound with which the cable is treated.Only a small amount of scale or other wax should be used because it isrelatively inflammable. After being assembled the parts previouslydescribed are passed through a machine which applies to them theover-all cotton braid coating or covering 16. This covering tightlyholds the various parts in place.

The cable with its over-all braid is then saturated with a hot compoundsimilar to that used for the jute wrappings, which is flame-proof incharacter and which completely penetrates the fibers of the over-allbraid 16 and alsov of the longitudinal jute fillers 14 to a greater orless degree.

This compound or saturant has an asphalt base and also has a highermelting point than that of the protective coating of scale wax on thejute wrappings and is applied at about 500 F. with the result that whenthe wax melts it somewhat increases thefluidity of that portion of thesaturant which finds it way through the over-all braid into theinterstices between the various elements of the cable. I After thesaturant is applied to the cable it is run through a heated steel.wiping die which forces the mate rial through the fibers of the braid,sizes the cable and also smooths its outer surface. When the saturanthardens it renders all the material inside of the over-all braid ornon-metallic sheath practically solid. Mention has been made of thespecially strong fillers or members 14 and 15 to give increased tensilestrength to the cable. They also have another and very useful purpose,

i. e., they are or may be used to split the over-all braid or sheathwhen necessary to remove the same. In some cases-the wireman has toremove ten to twelve inches of insulating covering in making aconnection and in other cases as much as three feet. With the fillersarranged as described, as soon as the end of a filler is made accessibleit can be easily removed.

After the saturator has set the cable is further treated b being given acoating of finishing wax which was a high melting point, say of theorder of 380 F. To make the cable as smooth as possible to facilitatedrawing into building partitions, etc. the cable may be given a coatingof mica dust, which has a slight lubricating effect. After receiving thecoating of mica dust the cable is passed through ironing rolls, afterwhich it may be reeled.- After being cooled the cable may be again runthrough ironing rolls to give it the final finish. A so called slickfinish may be given to the cable by using scale wax after the finishingcompound, but it should be used sparingly because inflammable.

In Fig. 3 we have shown on a large scale three conductors 5, 6 and 17arranged in multiple with insulation and fillers between the variousparts constructed and arranged as described in connection with the otherfigures. sonably flexible the several conductors are spiraled or laid uplike the strands of a rope before the over-all braid is applied.

As stated at the beginning of this specification one of the primerequisites of a cable is its ability to withstand use in damp places. Acable constructed in accordance with our invention maybe completelysubmerged in water for twenty-four hours and will not gain more than 10%moisture. As regards being-flame-proof, the cable will withstand beingsubjected to the heat of a five-inch unsen burner for five periods offifteen seconds'each with similar periods between and will not flamemore than fifteen seconds after the last period in the Bunsen flame.

What We claim as new and desire to secure by Letters Patent of theUnited States, is, I 1. A cable comprising multiple conductors,

In order to render such a cable reaeach conductor being enclosed in abody of insulating material, a double wrapping of cords surrounding thematerial, one of said Wrappings being heavier than the other, a compoundwith which both wrappings are treated, the compound more fully enteringthe fibers of the outer than of the inner wrapping, a protective coatingbetween the said body and the inner wrapping to prevent the compoundfrom affecting said body, fillers which also form strong tension membersand sheath cutters, a braided over-all sheath, a protective coatingbetween the sheath and the cord wrappings, and a flameproofing compoundwith which the sheath is impregnated.

2. A cable comprising multiple conductors, each conductor. beingenclosed in a body of rubber, an identifying braid covering for therubber, a double wrapping of jute cords around the braid, said cordsbemg wrapped right and left handed, the cords of the outer layer beingsinged, a protective coating of wax between the braid covering and theinner cord wrapping, a compound with which the cords are treated, theinner cords having less compound than the outer cords, a protectivecoating for the outer cord wrapping, longitudinal fillers adjacent thecords, an over-all protective braid which holds the conductors andfillers in their respective positions, and a flame proof compound withwhich the over-all braid and the fillers are impregnated.

3. A cable comprising multiple conductors, each conductor being coveredby a Water-proof body of insulation, a braided covering for the body, aprotective coating for the braid, a double wrapping of jute cords, thewraps being wound right and left handed, a compound which fully impregnates the outer wrap and partially enters the inner Wrap, the outersurface of the cords of the outer wrap being singed, a protective coatinfor each of said outer wra in s longitudinal fillers which occupy spaceson opposite sides of the conductors and form strong tension members toincrease the tensile strength of the cable, a braided overall coveringof textile material which binds the conductors, their respectiveinsulations and fillers into a compact mass, and a flame proof compoundwhich saturates the braided covering and mixes with the protectivecoatings of the jute wraps to fill the small spaces between the jutewraps, the fillers and the braided over-all covering.

In witness whereof, we have hereunto set our hands this 17th day ofJune, 1927.

EDWARD H. LEWIS. CLIFFORD O. HULL.

